Thrust reversal systems are known for example from documents FR 2 935 444 and FR 2 935 354. Amongst the various thrust reversal principles implemented in aircraft turbomachines, reversal cascade systems are known, these being provided with passages oriented so as to direct the air obtained from the secondary duct forwards in order to generate the reverse thrust force. The air is forced out of this secondary duct by reverser doors which, in the active configuration of the system, at least partially close this flow duct.
On the other hand, in the inactive configuration, each reverser door is in a stowed position in which it forms part of the outer wall of the secondary duct, also known as the OFS (Outer Fixed Structure). More specifically, in this inactive configuration of the reverser system, each door constitutes part of this outer wall of the secondary duct, within a mobile outer nacelle cowling containing the reversal cascade. During the transition from the inactive configuration to the active configuration, the mobile outer cowling is displaced rearwards by actuators, so as to clear the cascade, and bring the reverser doors into their position of closing of the secondary duct, by means of appropriate mechanical kinematics.
Although this principle is extensively applied, it nevertheless suffers from a problem of aerodynamic disturbance of the flow of air which passes through the secondary duct in the inactive configuration of the system. In fact, in this configuration, the flow of air within the secondary duct is disturbed during its passage over the areas where the body of the mobile outer cowling and the reverser doors, which are added onto this body, meet. This disturbance produces drag as well as pressure losses within the secondary duct, which lead to a decrease in the overall performance of the turbomachine.